What is the best way to save my layered file when I am done? I use PSE and have been saving everything as .psd and .jpeg. I read somewhere that I should save as .tiff instead of .psd because it would preserve my layers and save space, but I have seen on the boards that people are saving whole layouts as .png, which I use only for elements....?

The only things I have as a png file are those that need to maintain a transparent background. So, if I've done a siggie, I'll save it as a png so it doesn't end up with a white box around it. Other than that, I save my layouts as psd and jpeg files. A tiff file will also preserve layers and save some space, but not a lot. I save my file first as a psd, then "save as" a jpeg. Then I open that file and change the size for the gallery and "save as" again, but adding either web or _72 to the file name so I know which one it is. Sounds like you're already doing it right.
I think of my psd file like I would a negative. I don't throw them away just because I've printed or posted them. I can't count how many times I've opened a psd and changed something on it-- even years later.

I save my layouts in progress as PSD files but once I'm finished with it, I save as TIFF. When you use the LZW/ZIP compression options, you actually end up with a file that's about 1/2 the size of the PSD file but it still has layers intact. If you have a pretty large hard drive, then it's no harm keeping your PSD files but if you're concerned about space, I find TIFF files to be a good solution.

The only things I have as a png file are those that need to maintain a transparent background. So, if I've done a siggie, I'll save it as a png so it doesn't end up with a white box around it. Other than that, I save my layouts as psd and jpeg files. A tiff file will also preserve layers and save some space, but not a lot. I save my file first as a psd, then "save as" a jpeg. Then I open that file and change the size for the gallery and "save as" again, but adding either web or _72 to the file name so I know which one it is. Sounds like you're already doing it right. I think of my psd file like I would a negative. I don't throw them away just because I've printed or posted them. I can't count how many times I've opened a psd and changed something on it-- even years later.

The only things I have as a png file are those that need to maintain a transparent background. So, if I've done a siggie, I'll save it as a png so it doesn't end up with a white box around it. Other than that, I save my layouts as psd and jpeg files. A tiff file will also preserve layers and save some space, but not a lot. I save my file first as a psd, then "save as" a jpeg. Then I open that file and change the size for the gallery and "save as" again, but adding either web or _72 to the file name so I know which one it is. Sounds like you're already doing it right. I think of my psd file like I would a negative. I don't throw them away just because I've printed or posted them. I can't count how many times I've opened a psd and changed something on it-- even years later.

If i want my lay out editable, should i save it as psd file?

You won't be able to edit a png file. Both psd and tiff file save the layers, but there are a few things a tiff file won't save. I read about it a few weeks ago, but can't remember exactly what it is that it doesn't save though. I have used both psd and tiff files and they are both editable enough for me.